In typical large sized display devices, there are LCD (Liquid Crystal Display device) and PDP (Plasma Display Panel).
Different from the PDP which is a spontaneous emission type, the LCD, having no light emitting device for itself, requires a separate backlight unit, essentially.
Depending on a position of a light source, in the backlight units used in the LCD, there are an edge lighting type backlight unit and a direct lighting type backlight unit. The edge lighting type backlight unit has the light source arranged at left/right sides or upper/lower sides of an LCD panel, for diffusing a light throughout the panel uniformly to have good uniformity of the light and to enable to fabricate a thin panel.
The direct lighting type, a technology generally applied to a display device larger than 20″, has a plurality of light sources arranged under the panel, to have better light efficiency than the edge lighting type, finding its application to a large sized display device which requires high brightness.
As the light source for the related art edge lighting type or the direct lighting type, CCFL (Cold Cathode Fluorescent Lamp) has been used.
However, the backlight unit of the CCFL has drawbacks in that a substantial amount of power is consumed by the CCFL, a poor color reproduction ratio is poor to be about 70% of the CRT, and environmental pollution is caused by mercury added thereto.
In order to resolve above problems, as a substitute for the CCFL, active researches on a backlight unit of LED (Light Emitting Diode) are being made.
The backlight unit of LED enables partial turn on/off of an LED array permitting significant reduction of power consumption, and to provide color reproduction exceeding 100% of the color reproduction range specification of the NTSC (National Television System Committee) allowing providing an excellent picture quality to the consumers.